Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "documentation: Traffic Capture methods"
  - documentation: Traffic Capture methods

    Created new chapter on Traffic Capture and added short descriptions and explanation for each of the three methods currently supported by VSPERF. Subchapters include Traffic Capture in the VM, Traffic for testing NICs with Hardware acceleration and Traffic Capture on the Trraffic Generator.

    JIRA: VSPERF-556

    Change-Id: I280c54aa73961e0bbb61b40e8fe476bd3e92ff7d
    Signed-off-by: Richard Elias <richardx.elias@intel.com>
    Reviewed-by: Martin Klozik <martinx.klozik@intel.com>
    Reviewed-by: Al Morton <acmorton@att.com>
    Reviewed-by: Christian Trautman <ctrautma@redhat.com>
    Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>
    Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>

diff --git a/docs/submodules/vswitchperf b/docs/submodules/vswitchperf
index 78de0c6..c870b4c 160000 (submodule)
--- a/docs/submodules/vswitchperf
+++ b/docs/submodules/vswitchperf
@@ -1 +1 @@
-Subproject commit 78de0c6b53db31ae0d77aaa79de015a73e981895
+Subproject commit c870b4c5e4360008e17dda745fc9ce11b212f702